Borescope with simultaneous video and direct viewing

ABSTRACT

An assembly is described for connection to a borescope to simultaneously provide a virtual image for direct viewing by an observer and a video image for viewing on a display. The assembly ( 10 ) comprises a body ( 12 ) with a distal end for connection to an insertion tube of a borescope and a proximal end providing an eye piece into which an observer may look. The body contains a relay lens ( 16 ) and an ocular lens ( 18 ). A beam splitter ( 28 ) is mounted in the optical path between the relay lens ( 16 ) and the ocular lens ( 18 ) and diverts a proportion of light received from the relay lens ( 16 ) to an image-to-video conversion device ( 30 ) mounted laterally to the optical path. The ocular lens ( 18 ), beam splitting device ( 28 ) and the image-to-video conversion device ( 30 ) are all located in a common mounting ( 38 ) which can be translated in a direction parallel to the optical path to allow for focussing.

[0001] The present invention relates to a borescope which simultaneouslyprovides a virtual image for direct viewing by an observer and a videoimage viewing on a display.

[0002] As used herein, the term borescope refers to any form of opticalinstrument used to form an image of an object at an inaccessible orinconvenient location and to transmit the image to another moreconvenient location for viewing. Such instruments are often referred toby other names such as endoscope, fibrescope, videoscope etc.

[0003] These instruments usually include an insertion tube, which may berigid or flexible, with a housing at the proximal end. An objective lenssystem at the distal end of the insertion tube forms an image of anobject. This is transmitted to the proximal end for viewing. Borescopesgenerally fall into two categories, that is those including visualsystems and those having video systems.

[0004] A visual system comprises three optical sections. First, anobjective lens system is provided at the distal end of the insertiontube. This may include a prism arrangement to change the direction ofview. The objective lens system forms an image of the object. Secondly,a relay system is provided which transfers the image from the distal endof the insertion tube to the proximal end. This may be a train of lensessuch as standard lenses, rod lenses or gradient index (GRIN) lenses, ora bundle of optical fibres. Thirdly, an ocular lens system is providedin housing at the proximal end of the scope. This takes the real imagefrom the end of the relay system and forms a virtual image for anobserver's eye to view at a comfortable distance away, typically onemetre, equivalent to −1 dioptre.

[0005] The benefits of a visual system include a high resolution image,a high dynamic range, i.e. the ability to see detail in both bright anddark areas of the image at the same time, a high brightness image,portability, lower cost and high temperature resistance of the insertiontube.

[0006] Video systems also comprise an objective lens system as in avisual scope, but in this case the image is formed on an image-to-videoconverter, such as a CCD (charge coupled device). The CCD turns theoptical image into an electrical signal which can be passed by cable tothe proximal end of the scope. An image processor is provided to processthe video signal into a form that can be viewed on a display, such as amonitor screen.

[0007] The benefits of a video system include the ability to record andmanipulate images and to display images on a screen and hence to have alarge magnification of the object under inspection and the ability formultiple viewers to see the image at the same time. It also leads to areduction in eye strain and a possible reduction in size of the housingof the scope, to allow the scope to be used in smaller spaces.

[0008] It is possible to attach a still or video camera to the eyepieceof a visual borescope to convert the image to a video signal. However,doing this removes the ability to examine a visual image at the sametime. This also increases complexity and cost, and adapters are requiredto connect the camera to the scope. The additional size of the cameraand adapter can also limit the usefulness of the scope in confinedspaces.

[0009] The present invention provides an assembly for a borescope,comprising a body having a distal end for connection to an insertiontube and a proximal end providing an eyepiece into which an observer maylook, the body containing a relay lens for receiving light from a relaysystem in the insertion tube, an ocular lens for creating a virtualimage for viewing by an observer and a beam splitter device mounted inthe optical path between the relay lens and the ocular lens and operableto divert a proportion of light received from the relay lens to animage-to-video conversion device mounted laterally to the optical path,and wherein the ocular lens, beam splitting device and image-to-videoconversion device are located in a common mounting translatable in adirection parallel to the optical path to allow for focussing.

[0010] In this way, the advantages of visual and video scopes can beachieved with a single, compact unit and focussing can be achievedsimultaneously for the visible image path and for the video image pathfor different working ranges of the scope.

[0011] Preferably, a collar is rotatably mounted on the body and coupledto the common mounting such that rotation of the collar causestranslation of the mounting in a direction parallel to the opt+

[0012] In a preferred embodiment, the beam splitter device is a beamsplitter cube operable to divert a proportion of light at substantially90° to the optical path.

[0013] Conveniently, the beam splitter device is operable to divertapproximately 50% of light received to the image-to-video conversiondevice.

[0014] Advantageously, the beam Splitter device is adjustable to alterthe proportion of light diverted to the image-to-video conversiondevice.

[0015] In one embodiment, the beam splitter device comprises a firstelement operable to transmit all light received from the relay lensalong the optical path to the ocular lens, a second element operable totransmit a first proportion of light along the optical path and todivert a second proportion of light to the image-to-video conversiondevice and a third element operable to divert all the light received tothe image-to-video diversion device, wherein the first, second and thirdelements are selectively moveable to position one element at a time inthe optical path.

[0016] In this way, depending upon the application, the user can selectwhether simultaneous visual and video images are obtained or whether tooptimise any one form of image.

[0017] Conveniently, the image-to-video conversion device comprises CCDboard camera which preferably comprises a full digital signal processingmeans, for compactness.

[0018] To accommodate use with borescopes that include a prism at thedistal end of the insertion tube for lateral viewing, the image-to-videoconversion device may be programmable to allow for correction of imageinversion.

[0019] Alternatively, the beam splitter device may be configured toensure an image received by the image-to-video conversion device hasbeen reflected an even number of times.

[0020] Additionally, an inversion correction device may be mounted inthe body proximal to the ocular lens, to ensure correction of the imageviewed directly by an observer.

[0021] To provide a clear defined edge to the image, a field mask ismounted in the optical path at the location of the final real image,between the last relay lens and the beam splitter device.

[0022] The present invention also provides a borescope comprising aninsertion tube connected to an assembly of the type described above.

[0023] The invention will now be described in detail, by way of exampleonly, with reference to the accompanying drawings in which:

[0024]FIG. 1 is a schematic cross-sectional view of the housing of aborescope in accordance with a first embodiment of the presentinvention;

[0025]FIG. 2 is a schematic side view of an arrangement of lenses andprisms for use in a second embodiment of the invention; and

[0026]FIG. 3 is a schematic perspective view of an arrangement of lensesand prisms for use in a third embodiment of the present invention.

[0027]FIG. 1 shows an assembly 10 provided at the proximal end of aborescope. The assembly 10 comprises a housing 12 and a handle portion14 which can be grasped by a user's hand. An insertion tube (not shown)is connected to the distal end of the housing 12, shown on the left handside in the figure.

[0028] The insertion tube contains a conventional visual system, that isa viewing window at the distal end, an objective lens system forming animage of an object and a relay system for transmitting the image to theproximal end of the insertion tube and into the housing 12 where thelast relay lens 16 of the relay system is mounted.

[0029] An ocular lens 18 is provided towards the proximal end of thehousing 12, shown on the right hand side in the figure. As is known inthe art, the last relay lens 16 and ocular lens 18 may each be a singlelens, or a combination of two or more lenses.

[0030] A focus collar 20 is rotatably mounted on the housing 12 and isdescribed further below.

[0031] If the scope has a lateral direction of view, i.e. it viewsobjects to the side of the insertion tube, it will contain a prism atthe distal end of the insertion tube which inverts the image. To correctthis inversion, a corrective system such as a dove prism 22 is provided,in this case, in the housing 12 proximal to the ocular lens 18.Furthermore, if the insertion tube is rotatable about its longitudinalaxis to provide orbital scanning, a scan control collar 24 may berotatably mounted on the housing 12.

[0032] Typically, illumination of an object being viewed is provided bya bundle of optical fibres transmitting light along the insertion tubefrom a light guide. In a conventional manner, a light guide connector 26can be incorporated in the handle 14 coupling the optical fibre bundle(not shown) to a cable from an external light source (also not shown).

[0033] Thus, as in a conventional visual system, in the borescope of thepresent invention light from the relay lens 16 is passed to the ocularlens system 18, through the dove prism 22 for correction and then to anobserver's eye positioned adjacent an eye piece at the proximal end ofthe assembly 10.

[0034] However, in addition, the present invention incorporates a beamsplitter device 28 mounted between the last relay lens 16 and the ocularlens 18. This diverts a proportion of the light received from the lastrelay lens 16 substantially perpendicular to the optical path betweenthe relay lens 16 and ocular lens 18, to an image-to-video conversiondevice such as a CCD 30 mounted at 90° to the optical path. The beamsplitter device 28 may be of any type, although it is currentlypreferred for this to be a beam splitter cube, formed of tworight-angled prisms with a coating on their interface plane.

[0035] A cable 32 connected to the handle portion 14 provides powerinput for, and receives a video output from, the CCD 30 for transmissionto a display monitor (not shown). Thus, at the same time that anobserver can directly view an image through the eyepiece, a video signalof the image can also be viewed on a display monitor.

[0036] Preferably, the system is designed to overfill the CCD 30, so asto give a full screen image on the display monitor. Also, to provide aclear defined edge to the image seen by an observer looking into theeyepiece, a field mask 34, i.e. a plate with a circular aperture, isplaced at the location of the final real image of the system, betweenthe last relay lens 16 and the beam splitter 28. The ocular lens 18 isdesigned to form a virtual image of both the field mask 34 and the finalimage at the same eye field of view as a conventional visual scope.

[0037] Preferably, the CCD 30 is mounted on a support column 36, itselfconnected to a mounting carriage 38 which carries the ocular lens 18,field mask 34 and beam splitter 28. This carriage 38 is translatable ina direction parallel to the main optical path through the scope. Thistranslation is achieved by the focus collar 20 which is coupled to thecarriage 38 so that rotation of the focus collar 20 causes lineartranslation of the carriage 38. Thus, focussing can be achievedsimultaneously for the CCD and the visible image paths for differentworking ranges of the scope. The lenses are designed such that the focustravel of both the CCD and ocular lens are the same for the requiredworking range of specifications of the scope.

[0038] Furthermore, the optical design is such that sphericalaberrations caused by the beam splitter device 28 are removed. Atelecentric design is used such that the light rays from the last relaylens 16 are all parallel, in order to remove off axis aberrations suchas astigmatism, coma and distortion that would otherwise be present whenusing a beam splitter device.

[0039] The image-to-video conversion device is a CCD board camera 30which has a full digital signal processor (DSP) set. This means that thedevice is compact and only requires a power input and a video outputcable 32. In the preferred embodiment, a power conversion board 40 isplaced in the handle portion 14 such that a voltage range of 7-30 voltscan be used as the input.

[0040] The CCD 30 is programmable to allow for correction of imageinversion which occurs if an odd number of reflections appears in thesystem, as when the scope has a prism at the distal end for lateralviewing.

[0041] Alternatively, the beam splitter 28 can be configured so as toensure an even number of reflections occur before light encounters theCCD 30, as shown in the second embodiment illustrated in FIG. 2. Here afirst reflection occurs in the prism at the distal end of the insertiontube, and a second reflection in a dove prism 44 which is part of therelay lens system. Thus, light passing to ocular lens 18 has undergonetwo reflections. The beam splitter 28 is arranged to provide two furtherreflections to ensure that the CCD receives an even number of imagereflections.

[0042] Typically, the beam splitter 28 will be configured to transmitapproximately 50% of light it receives through to the ocular lens 18,and to divert the other 50% of the light towards the CCD 30. However, itis anticipated that future CCD sensors may become more sensitive and ifso the ratio can be altered to maximise the image brightness for boththe visual and video systems.

[0043] Furthermore, in certain applications it may be preferable tomaximise the light throughput either through the visual or videosystems. In a third embodiment of the invention illustrated in FIG. 3,an additional device 46 is provided which provides three alternativeelements, mounted side by side. In the centre is a beam splitter cube28, which transmits a portion of light received from the relay lens 16on to the ocular lens 18 and diverts the remaining portion to the CCD.On one side, an element 48 such as a glass cube transmits all the lightand diverts none. On the other side, a third element 50, such as aprism, diverts all the light to the CCD 30 and transmits none to theocular lens 18. The dimensions of these elements 28, 48, 50 are suchthat the optical path length to the final image remains the same. Thedevice 46 can then be moved in a direction perpendicular to the opticalpath, as indicated by the arrows, such that a user may select whichelement 28, 48, 50 is placed in the optical path and thus whether allthe light is diverted to the CCD 30, or all the light is passed to theeye, or whether there is a split between the two.

[0044] Thus, the present invention provides a borescope with combinedvisual and video capability in a single compact arrangement. Thebenefits of both visual and video systems are available simultaneously.The skilled reader will appreciate that a number of alterations andmodifications may be made to the precise details prescribed, withoutdeparting from the scope of the invention as set out in the claims.

1. An assembly for a borescope, comprising a body having a distal endfor connection to an insertion tube and a proximal end providing aneyepiece into which an observer may look, the body containing a relaylens for receiving light from a relay system in the insertion tube, anocular lens for creating a virtual image for viewing by an observer anda beam splitter device mounted in the optical path between the relaylens and the ocular lens and operable to divert a proportion of lightreceived from the relay lens to an image-to-video conversion devicemounted laterally to the optical path, and wherein the ocular lens, beamsplitting device and image-to-video conversion device are located in acommon mounting translatable in a direction parallel to the optical pathto allow for focussing.
 2. An assembly as claimed in claim 1, furthercomprising a collar rotatably mounted on the body and coupled to thecommon mounting such that rotation of the collar causes translation ofthe mounting in a direction parallel to the optical path.
 3. An assemblyas claimed in any preceding claim, wherein the beam splitter device is abeam splitter cube operable to divert a proportion of light atsubstantially 90° to the optical path.
 4. An assembly as claimed in anypreceding claim, wherein the beam splitter device is operable to divertapproximately 50% of light received to the image-to-video conversiondevice.
 5. An assembly as claimed in any preceding claim, wherein thebeam splitter device is adjustable to alter the proportion of lightdiverted to the image-to-video conversion device.
 6. An assembly asclaimed in any preceding claim, wherein the beam splitter devicecomprises a first element operable to transmit all light received fromthe relay lens along the optical path to the ocular lens, a secondelement operable to transmit a first proportion of light along theoptical path and to divert a second proportion of light to theimage-to-video conversion device and a third element operable to divertall the light received to the image-to-video diversion device, whereinthe first, second and third elements are selectively moveable toposition one element at a time in the optical path.
 7. An assembly asclaimed in any preceding claim, wherein the image-to-video conversiondevice comprises a CCD board camera.
 8. An assembly as claimed in claim7, wherein the CCD board camera comprises a full digital signalprocessing means.
 9. An assembly as claimed in any preceding claim,wherein the image-to-video conversion device is programmable to allowfor correction of image inversion.
 10. An assembly as claimed in any ofclaims 1-8, wherein the beam splitter device is configured to ensure animage received by the image-to-video conversion device has beenreflected an even number of times.
 11. An assembly as claimed in anypreceding claim, further comprising an inversion correction devicemounted in the body proximal to the ocular lens.
 12. An assembly asclaimed in any preceding claim, further comprising a field mask mountedin the optical path at the location of the final real image, between thelast relay lens and the beam splitter device.
 13. A borescope comprisingan insertion tube connected to an assembly as claimed in any precedingclaim.
 14. An assembly for a borescope substantially as herein beforedescribed and with reference to the accompanying drawings.